Here's a summary. For what it's worth, I'm not necessarily endorsing any or all of these. I'm simply collating the views of a number of political and military people I've heard on the issue.

Politicisation of the military:Service chiefs traditionally stay out of party politics, and for good reason: the military serves the whole nation, not a section of it. There is real unease among the senior military about Sir Richard’s move, even greater than that felt over Lord West’s decision to serve as a minister, because there was never any suggestion that Lord West favoured Labour while he was First Sea Lord. One senior military type tells me he fears Sir Richard’s decision will mean that ministers (of any party) will never again fully trust the service chiefs: there will always be a doubt in their minds, he says. And that cannot be good for sensible defence policy.

Diminishing returns: Hitherto, Sir Richard’s words carried weight because he had credibility and impartiality. Now, he faces a legitimate question: is he speaking because of his beliefs or because of his party allegiance? Front-page stories will be much harder to come by now he’s ceased to be neutral.

Working relations:How will the new Conservative defence advisor work along with the current service chiefs? They may feel, not unreasonably, that it is their job to provide military advice to ministers on current operations. If, say, Gen Sir David Richards, the current CGS, advises one course of action and Sir Richard another, whose counsel will carry more weight?

Blowback: Sir Richard has strong views about military resources. The Tories will have to cut the defence budget. Will he sit quietly as that happens? Sir Richard did Labour a lot of damage when he thought the party wasn’t doing enough for defence. Could he one day inflict similar harm on the Tories?

History:As CGS, Sir Richard was party to a lot of controversial military decisions, all carefully minuted and documented. Some MoD people are privately seething that he has publicly criticised things that, they say, he signed off. What if those decisions start to come to light? His record in office must now be reassessed in the light of his new position.

Internal tension: If, as many expect, Sir Richard ultimately becomes a defence minister, how will he work with other Tory defence bods? Liam Fox will publicly welcome the move, but colleagues believe that he’s privately anxious about a lot of the issues here, and, perhaps, his own position. The reports that Sir Richard ultimately wants to be defence secretary won’t help.